A case of basidiobolomycosis mimicking rhabdomyosarcoma: A diagnostic challenge

Basidiobolomycosis is a rare curable fungal infection caused by the saprophytic fungus Basidiobolus ranarum. It often causes skin infections but rarely infects visceral tissues in humans. Gastrointestinal basidiobolomycosis is an emerging form, which is rare but is increasingly reported. Due to its ability to mimic more common diagnoses such as chronic inflammatory disorders and malignancies, Basidiobolomycosis imposes a diagnostic challenge on most physicians. Therefore, a timely and correct diagnosis by laboratory tests and careful review of images along with proper medical management can save patients from invasive treatments and reduce both morbidity and mortality. Here, we present a rare case of an 8-year-old boy with basidiobolomycosis initially misdiagnosed as rhabdomyosarcoma. We aim to highlight basidiobolomycosis as a potential differential from masses on imaging under the right clinical circumstances and to provide radiologists with key imaging details to help recognize this infectious etiology and reduce its associated morbidity.


Introduction
Basidiobolus ranarum is an environmental saprophytic fungus found in dead plant material, rotten wood, soil, reptile feces, insectivorous fish, and amphibians, and is mainly limited to tropical regions; the Middle East, Africa, and South America [1] . It belongs to the order Entomophthorales of the class Zygomycetes. Basidiobolomycosis is characterized by chronic testinal, or systemic lesions [4] . Consequently, gastrointestinal basidiobolomycosis (GIB) is recognized in the literature as a cause of misdiagnosis due to its ability to mimic the manifestations of more common entities such as benign tumors, malignancies, inflammatory bowel disease, appendicitis, tuberculosis, etc. [2] .
Due to the varied presentations associated, several diagnostic modalities have been used to identify the cause. Medical imaging has been commonly used to identify the cause of symptoms in patients with basidiobolomycosis who had not yet received this curable diagnosis; In a recent study with a moderate sample size of 30 patients, 68% have performed computed tomography in their study [2] .
In hope of better identification of basidiobolomycosis with the aim of reducing associated morbidity and mortality [1] , we here present a case in which the infection was initially misdiagnosed as rhabdomyosarcoma, with an emphasis on its radiological findings that have raised suspicion of an infectious cause rather than malignancy later on. Upon review of the literature, only 7 similar cases have been reported between 2012 and 2022, some of which have stated rhabdomyosarcoma as an initial differential to the mass formed by Basidiobolomycosis [5] . We aim to highlight basidiobolomycosis as a potential differential to masses on imaging under the right clinical circumstances [6] , so we can provide the appropriate therapy as soon as possible, as the duration of morbidity of this infection can last months [2] .

Case presentation
An 8-year-old male patient from the southern province of Saudi Arabia presented to a local hospital with perianal pain, constipation, and gluteal swelling for 3 months. He also reported intermittent low-grade fever. He was diagnosed with gluteal abscess and underwent an incision only. He was discharged on antibiotic; however, no improvement was noticed. Pelvic magnetic resonance imaging (MRI) was performed and bladder and gluteal masses were found. He was referred to our hospital as a potential case of rhabdomyosarcoma. On arrival, he complained of on and off fever, decreased oral intake, dysuria, and frequency with a small amount of urine. He also complained of back pain that was partially relieved by acetaminophen. Physical examination showed an ill, febrile and underweight child with a firm erythematous gluteal mass extending to the peri-anal area with bilateral inguinal lymphadenopathy.
Laboratory investigations showed hemoglobin (10. Blood and urine cultures were negative. A series of images including ultrasound, CT scan, MRI and PET/CT scan were performed and a mass arising from the bladder base/prostate with intravesical extension likely representing bladder base rhabdomyosarcoma with tumor extension to the left pelvic sidewall and inversion to the internus muscle of the left obturator. Additionally, a large left gluteal subcutaneous mass and bilateral enlarged inguinal lymph nodes suggested metastasis ( Figs. 1-4 ) Ultrasound showed echogenic kidneys with left hydroureteronephrosis.
An initial diagnosis of rhabdomyosarcoma and acute kidney injury secondary to obstructive uropathy and contrastinduced injury was made. Accordingly, the patient was scheduled for biopsy, Port A Cath insertion, and bilateral nephrostomy tube insertion. He was started on empirical antibiotics for the fever and high white blood counts. Cystoscopy guided bladder neck and posterior urethral biopsies showed benign urothelium with polypoid cystitis and acute and chronic inflammations. The biopsies were probably not representative and inconsistent with the radiologically described possible rhabdomyosarcoma. Therefore, the patient was referred for lymphoma workup and scheduled for bone marrow biopsy and repeated cystoscopy-guided biopsy. The bone marrow biopsy result showed normocellular bone marrow with 90% cellularity without morphological evidence suggesting leukemia, lymphoma, or nonhematopoietic malignancies.
Upon a second review of the images by different radiologists to delineate the nature and source of the mass by analyzing and comparing different imaging modalities, a suspicion of infectious/inflammatory cause was raised due to several findings. The presence of the intersphincteric fistulous tract associated with focal left gluteal collection as shown on PET / CT, MRI, and ultrasound ( Fig. 5 ). As a result, the diagnosis of malignancy and necrosis was less likely.
Radiologist recommended a pelvic ultrasound-guided biopsy and the results showed mixed acute and chronic inflammation with multinucleate giant cells and prominent eosinophils. Periodic acid-Schiff (PAS) and Grocott methenamine silver (GMS) stains highlight hyphal fungal organisms suggesting basidiobolomycosis ( Fig. 6 ). The patient was started on a prolonged course of Voriconazole with excellent response. Laboratory investigations showed a marked improvement in the patient's blood and kidney functions. Complete resolution of the bladder and gluteal masses was noted in ultrasound follow-up ( Fig. 7 ), which saved him from invasive surgical resection of the mass.

Discussion
Basidiobolomycosis is a rare emerging fungal infection caused by Basidiobolus ranarum. In the literature, more than 102 cases of GIB published between 1997 and 2018 and reviewed by Mohammadi et al. [1] . It belongs to the Zygomycetes class, which includes 2 fungal orders: Mucorales and Entomophthorales. The Mucorales include Mucor species and Entomophthorales include B. ranarum, which infect immunocompro- . It is generally found in a temperate and humid environment mainly in soil and decaying vegetables, and also in the intestines of some animals such as fish, dogs, and amphibians [ 2 ,10 ].
B. ranarum infects both adult and pediatric populations with male predominance, while the majority of pediatric cases were reported from Saudi Arabia [10] . Basidiolobolomycosis commonly causes a characteristic subcutaneous lesion mainly in the trunk, buttocks, or extremities [11] . It rarely causes visceral lesions; however, gastrointestinal and pelvic involvement has become an emerging manifestation of B. ranarum infection. The involvement of primary gastrointestinal sites includes the colon, stomach, and small intestine [12] . Common presentation of basidiobolomycosis includes fever, abdominal pain, constipation, and abdominal mass. Many factors contribute to the difficulty in diagnosing GIB, including nonspecific clinical presentation, the absence of predisposing risk factors, and suboptimal biopsy results. Therefore, it is often misdiagnosed as malignancy, intestinal tuberculosis, or inflammatory bowel disease.
Most reported cases showed masses located in the colon, liver, small bowel, or multiple locations, and concentric bowel wall thickening on abdominal imaging, mainly CT. Therefore, the differential diagnosis of neoplasms and IBD was initially suggested [6] . Additionally, some cases reported abscess for-mation implying a potential infectious cause such as tuberculosis. Meanwhile, our case showed a large pelvic mass that was difficult to identify its origin with a subcutaneous gluteal lesion that was first mistaken for rhabdomyosarcoma. It is important to remember that rhabdomyosarcoma is the most common pelvic soft tissue sarcoma in children. It usually arises from the genitourinary system and commonly affects the bladder [13] . Generally, MRI findings of rhabdomyosarcoma often show hypointense to isointense on noncontrast T1-weighted images and isointense to hyperintense on T2weighted sequences. They frequently have areas of hyperintensity without enhancement representing necrosis on water sensitive sequences [14] . Furthermore, regional and distant lymph node metastases may be present that mimic lymphoma or epithelial malignancies [14] . However, it is less likely to present with an intersphincteric fistula, as seen in our case. It is worth mentioning the trigger findings that suggested an infectious cause rather than rhabdomyosarcoma in our case, as an intersphincteric fistulous tract associated with focal left gluteal collection was seen.
A high index of suspicion of GIB should be maintained in the differential diagnosis of patients with abdominal mass, subcutaneous lesion, and eosinophilia along with a negative biopsy for neoplasms. In addition to findings suggestive of infectious/inflammatory changes such as fistulas and collections on radiographic images. The gold standard diagnosis of basidiobolomycosis is the histopathologic evaluation of the biopsy [1] . The treatment modality mentioned in the literature     ranged between medical and surgical intervention [ 15 ,16 ]. It is important to state that the prolonged course of antifungal medication from the -azole family showed complete resolution of infection [ 15 ,17 ] follow-ups without surgical interventions.
We emphasize the importance of early recognition of this rare fungal infection by carefully evaluating different imaging modalities. Thus, preventing patients from undergoing unnec-essary surgical intervention and reducing complications and morbidity.

Provenance and peer review
Not commissioned, externally peer-reviewed

Ethical approval
Patient anonymity is maintained throughout this manuscript, and consent was obtained for publication from the patient Author contribution R.A., A.A., F.S., B.N.S., M.M.A. drafted the manuscript B.N.S contributed to reviewing and finalizing the manuscript. F.S. provided the imaging findings and their interpretation for the case presentation section. All authors reviewed the manuscript for intellectual content and approved the submission.

Consent for publication
Written informed consent was obtained from the patient's family for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Patient consent
Written informed consent was obtained from the patient's family for publication of this case report and accompanying images. Patient anonymity is maintained throughout this manuscript.